Control arrangement for an alkaline pressure electrolyzer

ABSTRACT

In a control arrangement and a method for controlling an alkaline pressure electrolyzer including gas spaces for receiving the H 2  and O 2  gases generated by the pressure electrolyzer, a manual control input and an integrally operating controller for at least one of the control values gas pressure and fill level difference of the gas spaces, and an uncoupling network which provides control inputs for independently controlling at least one of the fill level difference and the gas pressure in the gas spaces, hydrogen and oxygen blowdown valves in communication with the respective gas spaces are controlled such that the blowdown flows of the hydrogen and the oxygen from the respective gas spaces are at a ratio of 2:1 and the sum of the blowdown gas flow volume change is zero.

BACKGROUND OF THE INVENTION

[0001] The invention relates to a control arrangement for an alkaline pressure electrolyzer including controllers for the control values fill level and gas pressure and to a method of controlling an alkaline pressure electrolyzer.

[0002] An electrolyzer generally includes a plurality of electrolytic cells arranged in series for example as disclosed in DE 196 07 235 C1.

[0003] For a better understanding of the art, FIG. 1 shows a pressure electrolyzer of the state of the art. It shows an electrolyzer block 20 including an alkaline solution and consisting of a stack of a plurality of identical cells, each having an anode 11, a cathode 12 and an ion-permeable diaphragm 13. The stacked cells have good electrical conductivity and are interconnected in a gas-tight manner.

[0004] An operating medium is added to an electrolyte, supplied to the electrodes and dissociated into its components (product gases). By the introduction of electrical energy (for example, from renewable sources such as wind or the sun) the electrolysis process is initiated whereby., under high pressure, hydrogen, H₂, is released at the cathodes 12 and oxygen, O₂, is released at the anodes 11. The product gases H₂ and O₂ of all the electrolytes cells are separately collected and conducted away whereby a mixture of H₂ bubbles and an alkaline medium reaches a gas separator 36 by way of the conduit 30 and a mixture of O₂ bubbles and an alkaline medium reaches the gas separator 37 by way of the conduit 31. In the gas separators 36 and 37, the gases are separated from the alkaline medium which is returned to the electrolytes block 20 by way of the return line 35.

[0005] The gas or gases produced thereby can be conducted from the gas separators to a storage (for example, a hydrogen tank, hydride storage element) under pressure. From there, the gas can be retrieved and bottled (not shown).

[0006] The gas separator 36 forms, together with the gas separator 37 and the connection 34, a system comprising two communicating tubes, which are filled with the alkaline columns 28 and 29 up to the fill levels 24 and 25. The arrangement separates the H₂ gas space 26 from the O₂ gas space 27 and, because of the movability of the alkaline columns 28 and 29, permits pressure equalization between the gas spaces 26 and 27. Such pressure equalization is necessary because of the pressure sensitivity of the diaphragm 13.

[0007] Control values for the operation of the electrolyzer are the gas pressure in the whole system and the fill level difference in the gas separators. With non-stationary electrolysis operation, there are relatively high requirements for operational quality.

[0008] The gases H₂ and O₂ produced in the electrolyzer block 20 increase the pressure in the gas spaces 26 and 27 and affect, depending on the geometric design of the gas separator 36, 37, more or less the fill levels 24 and 25 and, consequently, the fill level difference.

[0009] During electrolysis, the fill level of the electrolyte in the gas separators is routinely monitored for operational and safety reasons. The average fill level is utilized for controlling the operating medium amount supplied to the electrolyzer. In a water electrolyzer, for example, water is added when the fill level has become too low. Also, the emergency shut down system of the electrolyzer may be based on the fill level of the operating medium. By operating the H₂, blow-down valve 22 or the O₂ blow-down valve 23, the gas pressures in the gas spaces 26 and 27 and the fill levels 24 and 25 can be controlled. The fill levels 24 and 25 however must be controlled automatically because of the danger of an oxy-hydrogen explosion as a result of a mixing of H₂ and O₂ when the fill level difference is too large. A suitable control arrangement is provided for this purpose, which also controls the gas pressure, wherein the changes of the gas volume flows in the conduits 30 and 31 affect the control values as disturbance variables.

[0010] From Mohr et al. (P. Mohr, V. Peinicke, and T. Welfouder, 1996, “Konzeption und Realisierung der Druckregelung eines solar betriebenen Elektrolyseurs”, in Automatisierungstechnische Praxis 38, Heft 9, 42-48) a control arrangement for an electrolyzer is known (FIG. 2).

[0011] In addition to the control circuits for the gas pressure and the fill level difference shown in FIG. 2, FIG. 1 shows the electrolysis gas separation system 21, the H₂ blow-down valve 22 and the O₂ blow-down valve 23 which are also shown in FIG. 2.

[0012] The fill level difference control circuit of FIG. 2 includes the fill level measuring arrangement 51, which retrieves from the electrolysis gas separation system 21 the momentary information 52 concerning the fill level 25 in FIG. 1 and converts this information to the corresponding electrical actual value signal 54 for the fill level difference. This signal is compared in the comparator 66 with the desired value 68 for the fill level difference. The difference is supplied to the controller 64 for the fill level difference whose control output 70 is connected to the input 58 of the H₂ blow-down valve 22 by way of the jointure 99 a.

[0013] The gas pressure control circuit as shown in FIG. 2 includes a pressure measuring device 55, which obtains the momentary gas pressure information from the electrolysis gas separation system 21 and converts the information to a corresponding electrical actual value signal 57 for the gas pressure. The signal 57 is supplied to a comparator 67 for comparison with a desired gas pressure value 69. The differential control signal is supplied to the controller 65 for the gas pressure whose control output 71 is connected to a control action input 59 of the O₂ blow-down valve 23 by way of a connecting point 99 b.

[0014] The controllers 64 and 65 in FIG. 2 are, in accordance with the state of the art, conventional PID controllers with proportional, integral and differential transmission components and, by controlling the blow-down valves 22 and 23, are to influence the blow-down flows 32 and 33 in such a way that the control values gas pressure and fill level difference do not stray from the predetermined desired values even during instationary operation of the pressure electrolyzer.

[0015] It is however a disadvantage of this control arrangement that, in practice, the control oscillations are not sufficiently damped. The gas pressure spaces 26 and 27 shown in the area 21 of FIG. 1 represent the integral parts of the control system areas, which, as is known in the control technology, cannot be satisfactorily controlled by controllers with integral components since their dynamic quality is already at the stability limit. However, the I component of the PID controller is needed if the disturbances effective on the control values, that is the changes of the electrolytes performance, are to be attenuated effectively.

[0016] Another disadvantage of this control arrangement is that it does not support manual operation of the pressure electrolyzer. Manual operation may be necessary for initial operation or during maintenance of the electrolyzer and is initiated by severing the connecting points 99 a and 99 b and supplying manually controllable signals to the control inputs 58 and 59. However, it is difficult with these manual control signals to adjust the control values gas pressure and fill level difference in a well defined manner or to maintain them constant since both control signals affect at the same time both controlled variables. Manual control is particularly difficult since the system is close to the stability limit anyhow. For safety reasons, a one-to-one coordination of control signals and controlled variables and a stabilization of the control system is therefore desirable.

[0017] It is the object of the present invention to provide a control system which has an improved control behavior and which permits safe manual operation.

SUMMARY OF THE INVENTION

[0018] In a control arrangement and a method for controlling an alkaline pressure electrolyzer including gas spaces for receiving the H₂ and O₂ gases generated by the pressure electrolyzer, a manual control input and an integrally operating controller for at least one of the control values gas pressure and fill level difference of the gas spaces, and an uncoupling network which provides control inputs for independently controlling at least one of the fill level difference and the gas pressure in the gas spaces, hydrogen and oxygen blow-down valves in communication with the respective gas spaces are controlled such that the blow-down flows of the hydrogen and the oxygen from the respective gas spaces are at a ratio of 2:1 and the sum of the blow-down gas flow volume change is zero.

[0019] With the control arrangement according to the invention, the operational safety of the electrolyzer and the control quality are substantially improved.

[0020] As means for independently influencing the controlled variables an uncoupling network may be used which includes control inputs for independently influencing the controlled variables fill level difference and gas pressure.

[0021] The uncoupling network provides for an uncoupling of manual control inputs of the control values fill level difference and gas pressure whereby manual control actions can be performed without danger.

[0022] In order to ensure that the controlled variables gas pressure and fill level difference can be controlled independently of one another the uncoupling network comprises transmission blocks, summing devices and, if necessary, a constant voltage source. The transmission blocks provide the transmission factors needed for the uncoupling effect. In each case, two summing devices are provided which form the input signals and the output signals of the uncoupling network. The voltage source is needed for the uncoupling of control circuit sections with so-called equal percent blow down valves. In this way, the uncoupling network becomes usable also for equal-percent characteristic valve performance graphs.

[0023] Particularly at least four summing devices and at least four transmission blocks together with a stationary voltage source can be so utilized that an uncoupled manual control of the fill level difference and the gas pressure can be performed.

[0024] As control means also P-controllers may be provided which stabilize the controlled variables fill level difference and/or gas pressure.

[0025] The controlled variables fill level difference and gas pressure are expediently so influenced that, with the occurrence of disturbances, they react with a finite change of the actual values. This means that the control sections of the fill level difference and the gas pressure provided with P-controllers have a proportional behavior and are consequently far from the stability limit.

[0026] The control system includes expediently an uncoupling network and also a P-controller. The uncoupling network does not need to be, but it may be, utilized together with one or both P-controllers. If both control mechanisms, that is the uncoupling network and one or both P-controllers, are utilized together, the control means support each other, that is, they influence the control values in such a way that they contribute together to an increased operational safety and to the control quality. In this way acceptable control results are achieved even with not optimally dimensioned control mechanisms.

[0027] In another embodiment of the invention, the control arrangements include P-controllers which, besides the inputs for the connection of the PID controllers, include each an additional desired value input. In this way, the control processes can be accelerated past the PID controllers if the integral components of the PID controllers result in unsatisfactorily slow control actions.

[0028] With the method according to the invention, the hydrogen blow-down gas flow and the oxygen blow-down gas flow is adjusted to a ratio of 2:1. This ratio corresponds to the electrolysis gas flows occurring during electrolysis. In this way, the effects on the fill level difference is minimized so that it remains constant.

[0029] A change of the control signal for a control mechanism of the fill level difference designated as a manual control input may control the blow-down volume flows of the gases in such a way that the sum of the blown down gas flow changes is zero.

[0030] If for example the hydrogen blow-down volume flow is in creased by a certain amount, the oxygen blow-down volume flow is reduced at the same time by the same amount. By this method step, the gas pressure is maintained constant.

[0031] If both control steps are utilized together, the control steps are uncoupled and have no influence on each other if gas pressure and fill level difference are to be adjusted at the same time.

[0032] If the P-controller is operated by way of summing devices of the uncoupling network, the control steps are preferably automatically uncoupled. Preferred embodiments of the invention will be described below on the basis of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033]FIGS. 1 and 2 shows prior art arrangements,

[0034]FIG. 3 shows the control arrangement according to the invention, and

[0035]FIG. 4 shows a control arrangement according to the invention with operational amplifiers.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0036]FIG. 3 shows a control arrangement 99 with an uncoupling network according to the invention which comprises transmission blocks 84, 85, 86, and 87, summation devices 88, 89, 92 and 93 and a voltage source 90. The uncoupling network, upon maintaining two so-called uncoupling conditions, causes the output signal of the summation device 93 to exclusively control the gas pressure, and the output signal of the summation device 92 to exclusively control the fill level difference.

[0037] The transmission blocks 84, 85, 86 and 87, the summation devices 88, 89, 92 and 93 and the voltage source 90 may consist of common electronic components such as operational amplifiers, resistors and condensers. Transmission blocks are characterized by certain signal transmission factors the summation devices by their summing functions with the transmission factor one and the voltage source by the electrical voltage provided at the outlet.

[0038] The uncoupling rule for the manual control input 95 for the gas pressure is for example: The transmission blocks 85 and 87 and the voltage source 90 are to be so dimensioned that the H₂ blow-down gas flow 132 and the O₂ blow-down gas flow 133 are, like the electrolysis gas flows, at a ratio 2:1. In this way, during manual control input for the gas pressure 95, the effect on the fill level difference is minimized.

[0039] The dimensioning of the transmission blocks 85 and 87 and of the voltage source 90 depends on the characteristics of the blow-down valves 122 and 123, which reflect the functional connections of the gas volume flows 132 and 133 with the control voltages 158 and 159. Assuming the H₂ gas volume flow 132 has the symbol vf₁₂₃; the valve control voltage, the symbol U₁₅₉, the O₂ volume flow 133 has the symbol vf₁₃₃, the valve control voltage has the symbol U₁₅₉, and the manual control voltage has the symbol U₉₅, the output voltage of the voltage source 90 is U_(9O) and the pressure differentials at the valves 122 and 123 are P₁₂₂ and P₁₂₃. Valve characteristics frequently occurring in chemical plants are linear or equal-percentage types.

[0040] For equal-percentage valve characteristics as functions of the valve lifts Y₁₂₂ and Y₁₂₃ the following equations are applicable:

Hydrogen side: vf ₁₃₂ =p ₁₂₂ ·K _(V122) ·exp{(Y ₁₂₂−1)·ln(ST ₁₂₂)}

y ₁₂₂ =f _(s) U ₁₅₈

oxygen side: vf ₁₃₃ =p ₁₂₃ ·K _(v123) ·exp{(Y ₁₂₂−1)·ln(ST ₁₂₃)}

y ₁₂₃ =f _(s) ·U ₁₅₉

[0041] The values for the flow coefficients K_(v122), K_(v123) and the setting ratios ST₁₂₂, ST₁₂₃ and also for the control factors f_(s) are provided in the data sheets of the valves 122 and 123. If, for simplicity reasons, the transmission factor one is used for the value 87, U₁₅₈=U₉₅ is obtained. With the uncoupling rule for 95 vf₁₃₂/vf₁₃₃=2 and the assumption p₁₂₂=p₁₂₃, a relation ship for the control voltage U₁₅₉ is obtained:

U ₁₅₉ =U ₉₅ ·K ₈₅ +U ₉₀

K ₈₅ =ln(ST ₁₂₂)/ln(ST ₁₂₃)

U ₉₀={1−K ₈₅ −ln(2·Kv ₁₂₃ /Kv ₁₂₂)/ln(ST ₁₂₃)}/f _(s)

[0042] Herewith the block 85 obtains the transmission factor K₈₅ and the voltage source 90 provides the constant value U₉₀.

[0043] For linear characteristics, the following equations can be provided:

Hydrogen side: vf ₁₃₂ =p ₁₂₂ ·Kv ₁₂₂ ·f _(s) ·U ₁₅₈

Oxygen side: vf ₁₂₃ =p ₁₂₃ ·Kv ₁₂₃ ·f _(s) ·U ₁₅₉

[0044] The values for the flow coefficients Kv₁₂₂, Kv₁₂₃ and the control factors f_(s) are given in the data sheets of the valves 122 and 123. With the uncoupling rule for 95 vf₁₃₂/vf₁₃₃=2, the assumption p₁₂₂=p₁₂₃ and with U₁₅₈=U₉₅, a relationship for the control voltage U₁₅₉ is obtained as follows:

U ₁₅₉ =U ₉₅ ·K ₈₅

K ₈₅ =Kv ₁₂₂/(2·Kv ₁₂₃)

[0045] The block 87 obtains again the transmission factor one, the block 85 obtains the transmission factor K₈₅, and for the voltage source 90, the voltage value U₉₀=0 is obtained.

[0046] The uncoupling rule for example for the manual control input 94 for the fill level difference is: the transmission blocks 84 and 86 are to be dimensioned in such a way that a change of the control signal 94 increases (or decreases) the H₂ blow-down volume flow 132 by a certain amount and decreases (or increases) at the same time the O₂ blow-down volume flow 233 by the same amount, that is, that the sum of 132 and 133 remains constant. The formula for the uncoupling rule 94 is:

Δvf ₁₃₂ +Δvf ₁₃₃=0

[0047] With the assumption that also the uncoupling rule vf₁₃₂/vf₁₃₃=2 for 95 is observed, by a differentiation of the equations for the valve characteristics according to the valve control signals 158 and 159, a functional connection between the control voltage changes ΔU₁₅₈ and ΔU₁₅₉ is obtained. If for 86 in accordance with the transmission block 87 for example the transmission factor one is used, ΔU₁₅₉=ΔU₁₅₉ is obtained, if ΔU₉₄ designates the change of the manual control 94.

[0048] For the equal-percentage valve characteristics, the following applies:

ΔU ₁₅₈ =ΔU ₉₄ ·K ₈₄

K ₈₄=−0.5·ln(ST ₁₂₃)/ln(ST ₁₂₂)

[0049] As a result, the block 84 obtains the transmission factor K₈₄. For linear value characteristics, independently of the uncoupling rule for 95, the following is obtained:

ΔU ₁₅₈ =ΔU ₉₄ ·K ₈₄

K ₈₄ =−Kv ₁₂₃ /Kv ₁₂₂

[0050] The block 84 obtains the transmission factor K₈₄.

[0051] With the uncoupling network consisting of the transmission blocks 84, 85, 86, and 87, the summing devices 88, 89, 92, and 93 and the voltage source 90, the controlled variables fill level difference and gas pressure can be controlled by way of the manual control inputs 94 and 95 in an uncoupled and therefore safe manner. Also, an improved automatic control behavior is achieved thereby. The control values gas pressure and fill level difference are controlled independently of each other.

[0052] Furthermore, the uncoupling network also enhances the control operation if the controllers 82 and 83 included in the control arrangement 99 of FIG. 3 and are effective via the summation devices 92 and 93.

[0053] The controller 82 is responsible for the stabilization of the fill level difference. It obtains information concerning the deviation of the actual value 154 of the fill-level difference from the desired value 168 by way of the comparison device 80. The controller 82 is a P-controller and causes the fill level difference, upon deviations, to react with a finite change of the actual value, that is, the control arrangement for the fill level difference provided with a P-controller has a proportional behavior and therefore is far from the stability limit.

[0054] The controller 83 is responsible for the stabilization of the gas pressure and obtains information concerning a deviation of the actual value 157 of the gas pressure from the desired value 169 by way of the comparison device 81. If it is a p-controller causing the gas pressure upon occurrence of disturbances to react with a finite adjustment of the actual value, the gas pressure control arrangement provided with the p-controller has a proportional behavior and therefore is far from the stability limit.

[0055] The dimensioning of the proportional coefficients 82 and 83 is not problematic and occurs in accordance with methods common in control engineering.

[0056] The stabilizing effects of the P-controllers support also the PID controllers 164 and 165 shown in FIG. 3. It is the object of these controllers to eliminate the residual control deviations of the P-controllers 82 and 83 by supplying the compensation signals 170 and 171 to the comparators 80 and 81. From the fact that the PID controller of FIG. 3 are connected in a circuit with proportional control arrangements instead of arrangements near their stability limits, as they are known from the state of the art, short control times and relatively small overshoot widths are obtained for the control values fill level difference and gas pressure.

[0057] The fill level difference control circuit of FIG. 3 further includes a fill level measuring arrangement 151, which obtains from the electrolysis gas separation system 121 the actual information 152 and 153 concerning the fill levels in the H₂ and, respectively, O₂ gas chambers and converts them into the corresponding actual value signal 154 for the fill level difference. This signal is compared in the comparator 166 with the desired value 168 for the fill level difference. The control difference is supplied to the controller 164 for the fill level difference whose control output 170 is connected by way of the comparator 80 of the controller 82 with the control input 158 of the H₂ blow-down valve 122 and with the control input 159 of the O₂ blow-down valve 123.

[0058] The gas pressure control circuit in FIG. 3 further includes a pressure measuring arrangement 155, which obtains from the electrolysis gas separation system 121 the actual gas pressure information 156 and converts it to the corresponding electrical actual value signal 157 for the gas pressure. The signal 157 is compared in the comparator 167 with the desired gas pressure value 169. The control difference is directed to the gas pressure controller 165. The output 171 of the controller 165 is connected, by way of the comparator 81 of the controller 83, to the control input 159 of the O₂ blow-down valve 123 and the control input 158 of the H₂ blow-down valve 122. The blow-down flows are represented by the reference numerals 132 and 133.

[0059]FIG. 4 shows a circuit for the control arrangement 99 of FIG. 3 provided with operational amplifiers. The reference numerals of the operational amplifiers, of the eight inputs and the two outputs correspond to the reference numerals of the respective components, inputs and outputs of the control arrangement 99 of FIG. 3. Operational amplifiers of the type OP741 are used. With the resistance R82, the amplification of the P-controller 82 is predetermined. With the resistance R83, the amplification of the P-controller 83 is determined. With the resistors R84 to R87, the transmission factors 84 to 87 of the uncoupling network are determined. With the potentiometer R90, the voltage source 90 is adjusted. All resistors which are not marked have constant values of 10 kΩ.

[0060] In another embodiment, the circuit arrangement of FIG. 4 is implemented as ANSI-C-Code in the integrated digital data acquisition system ADnC812 of the company Analog Devices. This system has eight analog inputs and two analog outputs. For a comfortable generation of the C-code, the circuit is simulated with the simulation program 20-sin 3.1 Pro of the company Controllable Products B.V., which is suitable for control engineering designs. From the operational model of the circuit, the program 20-sim 3.1 Pro generates the ANSI-C-Code. This code is treated and compiled with the development environment WE-dit32 of the company Raisonance S.A. The compiled program is transferred with its own loading program to the data acquisition system ADuC812 and is made there operational.

[0061] Listing of reference numerals concerning FIG. 1 (state of the art) 11, 12, 13 Anode cathode diaphragms 20 Electrolysis block 21 Electrolysis gas separating system 22, 23 H₂ blow-down value, O₂ blow-down value 24, 25 Fill level in the H₂, O₂ gas separator 26, 27 H₂ gas chamber, O₂ gas chamber 28, 29 Alkaline columns in the H₂ and O₂ gas separator 30, 31 Conduits to the H₂ and O₂ gas separator 32, 33 H₂, O₂ blowdown gas flows 34 Connection between the H₂ and O₂ gas separator 35 Return flow conduit in the electrolysis block 36, 37 H₂ gas separator, O₂ gas separator.

[0062] Additional reference numeral for FIG. 2, (State of the Art) 51 Fill level measuring device 52, 53 Information concerning the fill level in the H₂, O₂ gas spaces 54 Actual value signal for the fill level difference 55 Pressure measuring device 56 Actual gas pressure information 57 Actual value signal for the gas pressure 58, 59 Control input of the H₂, O₂ blowdown valve 64, 65 PID controller for fill level difference and gas pressure 66, 67 Comparator locations (desired value minus actual value for fill level difference and gas pressure) 68, 69 Desired values for fill level difference and gas pressure 70, 71 Control outputs of the PID controllers 64, 65 for fill level difference and gas pressure 99a Connecting point, interconnects control input 58 of the H₂ blowdown valve 22 and the control output 70 of the PID controller 64 in the fill level difference control circuit. 99b Connecting point, interconnects control input 59 of the O₂ blowdown valve 23 and the control input 71 of the PID controller 65 in the gas pressure control circuit

[0063] Reference numerals concerning FIG. 3 (control arrangement according to the invention): 80, 81 Comparator locations 82, 83 P-controller 84, 85, Transmission blocks 86, 87 88, 89, Summing devices 92, 93 90 Voltage sources 94 Manual control input for the fill level difference 95 Manual control input for the gas pressure 99 Control arrangement (dash-point lines) 121 Electrolysis gas separator 122, 123 H₂ blowdown valve, O₂ blowdown valve 132, 133 H₂, O₂ blowdown gas flows 151 Fill level measuring arrangement 152, 153 Actual fill level information for the H₂-, O₂ gas space 154 Actual value signal for the fill level difference 155 Pressure measuring device 156 Actual gas pressure information 157 Actual value signal for the gas pressure 158, 159 Control input of the H₂, O₂ blowdown valves 164, 165 PID controllers for the fill level difference and the gas pressure 166, 167 Comparator location (desired value minus actual value) 168, 169 Desired values for the fill level difference and the gas pressure 170, 171 Control outputs of the PID controllers 164, 165 for the fill level difference and gas pressure

[0064] Additional reference numerals for FIG. 4 (control arrangement with operational amplifiers according to the invention).

[0065] R82, R83, R84, R85, R86, R87—resistors

[0066] R90—potentiometer 

What is claimed is:
 1. A control arrangement for an alkaline pressure electrolyzer having gas spaces for receiving H₂ and O₂ gases, said control arrangement including integrally acting controllers for controlling the control variables fill level difference and gas pressure in said gas spaces, and means for independently influencing said control values.
 2. A control arrangement according to claim 1, wherein said means for independently influencing said control variables fill level difference and gas pressure comprises an uncoupling network (84, 85, 87, 88, 89, 92, 93) with control inputs.
 3. A control arrangement according to claim 1, wherein said uncoupling network (84, 85, 86, 87, 88, 89, 92, 93) comprises four transmission blocks (84, 85, 86, 87) with four transmission factors for establishing an uncoupling function and four summing devices (88, 89, 92, 93) for forming input signals for the uncoupling network and for forming control signals for controlling blow-down valves, which are in communication with said gas spaces for releasing gases therefrom.
 4. A control arrangement according to claim 2, wherein said uncoupling network (84, 85, 86, 87, 88, 89, 92, 93) includes a constant voltage source (90).
 5. A control arrangement according to claim 1, wherein a P-controller (82) is provided as means for controlling the fill level difference.
 6. A control arrangement according to claim 1, wherein said means for controlling said gas pressure includes a P-controller (83).
 7. A control arrangement according to claim 5, wherein said P-controller (82) includes a desired value input.
 8. A control arrangement according to claim 6, wherein said P-controller (83) includes a desired value input.
 9. A method of controlling an alkaline pressure electrolyzer having gas spaces for receiving H₂ and O₂ gases and including a manual control input (95) and an integrally operating controller (165) for the control value gas pressure in said gas spaces, an uncoupling network (84, 85, 87, 88, 89, 90, 92, 93), which provides control inputs for independently controlling a fill level difference and the gas pressure in said gas spaces, and hydrogen and oxygen blow-down valves in communication with said gas spaces for releasing H₂ and, respectively, O₂ therefrom, said method comprising the step of controlling the blow-down of said hydrogen and said oxygen from the respective gas spaces at a ratio of 2:1.
 10. A method of controlling an alkaline pressure electrolyzer including gas spaces for receiving H₂ and O₂ gases generated by said pressure electrolyzer, a manual control input (94) and an integrally acting controller (164) for the control value fill level difference, an uncoupling network (84, 85, 86, 87, 88, 89, 90, 92, 93), which provides control inputs for independently controlling the fill level difference of said gas spaces and the gas pressure therein and hydrogen and oxygen blow-down valves (122, 123) in communication with said gas spaces for releasing H₂ and, respectively, O₂ therefrom, said method comprising the step of controlling with a change of the control signal to the manual control input of the fill-level difference (94) the blow-down volume flows of gases from said gas spaces in such a way that the sum of the gas flow changes is zero.
 11. A method of controlling an alkaline pressure electrolyzer including gas spaces for receiving H₂ and O₂ gases generated by said pressure electrolyzer, a manual control input (94, 95) and an integrally acting controller (164, 166) for each of the control values gas pressure and fill level difference of said gas spaces, an uncoupling network (84, 85, 87, 88, 89, 90, 92, 93), which provides control inputs for independently controlling fill level difference and gas pressure in said gas spaces, and hydrogen and oxygen blow-down valves (122, 123) in communication with the respective gas spaces, said method comprising the steps of controlling said hydrogen and oxygen blow-down valves such that the blow-down volume flow from said hydrogen and oxygen gas spaces is at a ratio 2:1 and a change of the control signal for the manual control input of the fill-level difference causes the blow-down volume flows of the gases from the gas spaces such that the sum of the gas flow changes of the two flows is zero while concurrently influencing the control values fill-level difference and gas pressure independently of each other. 